The hormone melatonin, produced by the pineal gland, is thought to be involved in the regulation of human sleep, body temperature and circadian rhythms, but its mechanisms of action in these areas have not been fully clarified, while its clinical significance remains controversial. The proposed research will examine these issues from a novel perspective, by systematically assessing sleep parameters, core body temperature, cortisol secretion and residual melatonin levels in individuals who have undergone pineal resection. In addition to 24 days of rest-activity recordings through an actigraphy device, the study will consist of two sets of consecutive overnight sessions for the assessment of polysomnographic (PSG) sleep parameters and circadian rhythm parameters of core body temperature, plasma cortisol and melatonin, the latter as a measure of residual pineal functionality. A healthy sex- and age-matched control group will undergo the same procedures. The specific aims of this preliminary study are: (1) to characterize PSG sleep patterns and microstructure in subjects with impaired melatonin production relative to healthy controls; (2) to elucidate the relationship between sleep, melatonin and body temperature in the absence of normal pineal functionality; specifically, we propose to assess (a) whether very low or absent levels of melatonin are accompanied by a dampening of core body temperature rhythm; b) whether insomnia following pineal resection is accompanied by changes in cortisol secretion; (3) to assess the feasibility of the experimental protocol and to obtain data for calculating statistical power of key comparisons, with the future aim of performing larger scale, hypothesis-driven research.